The present invention relates to an apparatus for aligning the surface of a small component to be coplanar with a second component surface. Specifically, an air-bearing support which is capable of positioning a surface of a small circuit component parallel to a surface of an abutting component is described.
The present invention is directed to a common problem in microelectronic packaging technology. When fabricating electronic circuits by bonding small components together, there is a need to position the components to be coplanar with less than a 1 micron difference between surfaces of the components. The process of forming thermocompression bonds between leads of a component and corresponding circuit connections is one example of an application which requires an extreme degree of planarity between the silicon chip and the circuit leads. In the flip chip technology, microelectronic chips are placed face down on a silicon substrate and pressure is applied to the silicon chip in a uniform way, and the flip chip and silicon substrate are brought into coplanarity as a result of the applied pressure. If the planarity is not maintained the strength of the bond formed between leads of the chip and circuit component is directly affected.
An additional example of the need for positioning one component coplanar to another can be found in the liquid crystal art. A top glass is applied to a silicon or polysilicon substrate. The top glass and substrate are brought together under uniform pressure to reduce the gap between them to a few microns. If the surfaces are not maintained in a parallel condition, a difference of only 1 micron will produce an objectionable nonuniform performance of the liquid crystal element.
The problem of positioning components in a coplanar relationship has been addressed in U.S. Pat. No. 4,875,614. The alignment device described in this reference provides a surface for supporting a component which is capable of rotating in first and second perpendicular axes about a point that lies on the surface of the contact. The device provides a first carriage having a cylindrically concave surface which receives a second carriage having a complementary cylindrical convex surface. The two carriages are connected by roller bearing means which extend along first and second perpendicular directions between the two carriages. The second carriage supports a first component having a surface facing the surface of a second component. As the second component is brought into contact with the surface of the first component, the second carriage rotates in response to the force applied by the first component, thereby tilting the first component about two mutually perpendicular axes and establishing coplanarity between the first and second components.
The foregoing device has limitations with respect to positioning very small components. As component sizes decrease to a few millimeters on each side, an insufficient amount of torque may be generated to move the first carriage with respect to the second carriage due to friction between the roller bearings and the carriage surfaces.
Additionally, using the device of the foregoing patent with very small components results in the rotation of the first component as it is made coplanar with the contacting surface. While a coplanar relationship may be established, the resulting rotational misalignment between the two surfaces about an axis perpendicular to the two surfaces must be corrected with still other means associated with a component support.
The present invention provides for a solution to the foregoing problems which results from packaging very small components.